In order to make fiberglass products such as fiberglass doors look like they are made from wood, the fiberglass composite (i.e., the fiberglass/polymer binder mass) is colored with a suitable stain. Such stains are typically composed of various colorants and an organic solvent such as mineral spirits. Drying oils, which are liquid fatty acids capable of hardening to tough, solid films when exposed to air, are also normally included. A siccative, which is a metal salt of a short chain organic acid (e.g., cobalt di-(2-ethyl hexanoate)) is also normally included to cause the drying oil to cure, thereby forming a resinous binder for the colorant. Additional conventional ingredients may also be included.
The most commonly used drying oil used for this purpose is linseed oil, which typically contains ˜58% α-linolenic acid, ˜14% linoleic acid, ˜19% oleic acid, ˜4% steric acid and ˜5% palmitic acid. In some cases, the linseed oil is prepolymerized (“modified”) into a liquid resinous products before being used. For example, the linseed oil can be heated at elevated temperature, thereby producing “heat-bodied” linseed oil. Alternatively, the linseed oil can be co-polymerized with another monomer such as dicyclopentadiene. See, for example, U.S. Pat. No. 5,288,805 and U.S. Pat. No. 6,358,614, the disclosures of which are incorporated herein by reference.
Stains made with drying oils based on linseed oil, whether modified or unmodified, can take two to three days to cure when applied to fiberglass composites, since such composites do not absorb stains like natural wood. This represents a significant problem in practice because of the delay involved before the stain can be overcoated with another coat of stain and/or a protective clear coat such as polyurethane or the like.
Recently, Palmer International of Shippack, Pa., introduced a line of proprietary modified (prepolymerized) drying oil resins based on Cashew Nut Shell Liquid (CNSL). Although these liquid resinous products are said to provide low-VOC, air-drying wood stains capable of drying in as little as 4 to 5 hours, they dry too quickly to allow sufficient time for working these stains into fiberglass composite substrates, which is necessary when high quality, wood-simulating fiberglass doors are being made. Moreover, the adhesion of stains made with these products to fiberglass composite substrates is inadequate to be commercially viable.